I purchased foam bath letters from One Step Ahead for my two year old daughter. This set comes with every letter of the alphabet and ten numbers. They come in several different colors. They are made of a thick durable foam that is about a quarter inch thick and sticks to the side of the tub when they are wet. She liked playing with them during bath time and I thought it would be a great way for her to learn her numbers, letters, and colors.
I soon learned to hate these 36 pieces of colored foam floating around in the bathtub with my daughter. I ended up taking most of them out because putting them all in there at the same time was just too much. They are very difficult to store, because when bath time is finished they are wet. They do not stay stuck to the wall of the tub once they are dry, so if you try to store them there, they will end up in your tub.
So, while the educational value of these little foam nightmares is likely very high, the fact that at this very moment they are strewn about my entire house with little bite marks in them prevents me from being able to recommend them very highly.